It is not wise to connect an 8 Ohm loudspeaker directly to Arduino microcontroller pins. When we calculate the current through the speaker we get : I=V/R= 5V/8 ohm=0.625A=625 mA. But microcontroller pin can only drive 20 mA to 40 mA. So, this project can solve this problem. This amplifier can be used with music modules like WTV020SD.